@article{10_21136_CMJ_1983_101894,
     author = {Li, Qiao and Brualdi, Richard A.},
     title = {On minimal regular digraphs with girth 4},
     journal = {Czechoslovak Mathematical Journal},
     pages = {439--447},
     publisher = {mathdoc},
     volume = {33},
     number = {3},
     year = {1983},
     doi = {10.21136/CMJ.1983.101894},
     mrnumber = {718927},
     zbl = {0542.05035},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1983.101894/}
}